The present invention relates to a color cathode ray tube that incorporates a panel with a substantially flat outer surface, and a shadow mask.
In general, a color cathode ray tube includes a vacuum envelope having a substantially rectangular panel and a funnel. The panel has an effective section formed of a curved surface, and a skirt section standing from the periphery of the effective section. The funnel is jointed to the skirt section. On the inner surface of the panel effective section is provided a phosphor screen, which has non-emission black substance layers and three-color phosphor layers that are provided between the black substance layers and emit blue, green and red light. A substantially rectangular shadow mask is arranged inside the panel and opposed to the phosphor screen with a predetermined gap therebetween.
In the neck of the funnel, an electron gun is provided for emitting three electron beams. In the color cathode ray tube, three electron beams emitted from the electron gun are deflected by a magnetic field generated from a deflection yoke that is mounted on an outer surface of the funnel, thereby horizontally and vertically scanning the phosphor screen via the shadow mask to display a color image.
The shadow mask includes a mask main body, which has a substantially rectangular effective surface and a skirt portion extending from the periphery of the effective surface, and a rectangular mask frame fixed to the skirt portion of the mask main body. A large number of electron beam passage apertures are formed in the effective surface of the mask main body. These electron beam passage apertures cause the three electron beams, emitted from the electron gun, to reach selected portions of the three-color phosphor layer. The shadow mask is supported inside the panel by engaging, for example, holders attached to the corner sections of the mask frame, with stud pins provided on the corners of the skirt section of the panel.
In the above-described color cathode ray tube, in order to display a color image without color drift on the phosphor screen, it is necessary to accurately land, on the target three-color phosphor layers, the three electron beams passing through the electron beam passage apertures of the shadow mask. To this end, it is necessary to appropriately keep the distance (q value) between the inner surface of the panel effective section and the effective surface of the mask main body.
In recent years, a color cathode ray tube is being put to practice, in which the outer surface of the panel effective section is made to have a low curvature and therefore to be almost flat so as to enhance the visibility of display. In this color cathode ray tube, the greater the curvature of the inner surface of the panel effective section, the larger the difference in thickness between a central portion and a peripheral portion of the effective section. This is disadvantageous in light of display visibility. To avoid this, it is necessary to reduce the curvature of the inner surface of the panel effective section in accordance with the shape of the outer surface of the panel effective section. Further, in order to secure a xe2x80x9cqxe2x80x9d value appropriate for realizing appropriate beam landing, it is also necessary to reduce the curvature of the effective surface of the mask main body, opposed to the phosphor screen, in accordance with the shape of the inner surface of the panel effective section.
However, if the curvature of the effective surface of the mask main body is reduced, the mechanical strength of the mask main body is reduced, which means that the shadow mask will easily be deformed in the manufacturing process of the color cathode ray tube. Moreover, even after the color cathode ray tube is completed, the shadow mask will easily be deformed by an impact or a vibration applied thereto while it is transported. Also, when the color cathode ray tube is installed in a television set, it is possible that the shadow mask vibrates sympathetically with a sound emitted from a speaker, and hence the color purity of the image will degrade.
On the other hand, if the curvature of the effective surface of the main mask body is increased so as to avoid a reduction in its mechanical strength, it is necessary to increase the curvature of the panel effective section accordingly. In this case, the viewing angle is inappropriate, a displayed image is deformed, and a reflection image is easily formed on the inner surface of the effective section, thereby degrading the visibility of display. Furthermore, the brightness of a peripheral portion of the screen is reduced, thereby degrading the uniformity of a displayed image.
The present invention has been developed in light of the above-mentioned circumstances, and its object is to provide a color cathode ray tube, in which its shadow mask has a sufficient mechanical strength and which is improved in display visibility.
To obtain the above object, according to an aspect of the invention, there is provided a color cathode ray tube comprising: a vacuum envelope including a substantially rectangular panel having a substantially flat outer surface, an inner surface provided with a phosphor screen, and a long axis and a short axis perpendicular to each other and also to a tube axis; a shadow mask arranged in the vacuum envelope and opposed to the phosphor screen, the shadow mask including a mask main body that has a substantially rectangular mask surface and a skirt portion extending along a periphery of the mask surface, and a substantially rectangular mask frame attached to the skirt section of the mask main body, the mask surface including an effective portion opposed to the phosphor screen and provided with a plurality of electron beam passage apertures; and an electron gun provided in the vacuum envelope for emitting electron beams onto the phosphor screen through the shadow mask.
the inner surface of the panel has an effective section with a curvature, the inner surface of the panel being formed to satisfy at least one of the following relationships:
ZPH/LPHxe2x89xa60.050, 
and
ZPV/LPVxe2x89xa60.050 
where LPH represents a distance from a center of the effective section to a long axis end of the effective section, LPV represents a distance from the center of the effective section to a short axis end of the effective section, ZPH represents a fall of the effective section at the long axis end along the tube axis with respect to a level of the center of the effective section, and ZPV presents a fall of the effective section at the short axis end along the tube axis with respect to the level of the center of the effective section.
The mask surface has a pair of long sides situated symmetrical with respect to the long axis, and a pair of short sides situated symmetrical with respect to the short axis, at least one of each long side and each short side being curved such that a central portion thereof projects outwardly, and satisfying at least corresponding one of the following relationships:
YML/LMLxe2x89xa60.015, 
and
XMS/LMSxe2x89xa60.015 
where LML represents a distance from the short axis of the effective portion of the mask surface to each corner of the effective portion, LMS represents a distance from the long axis of the effective portion of the mask surface to each corner of the effective portion, YML represents a fall, along the short axis, between a point of each long side of the mask surface on the short axis and a point of the each long side which is apart from the short axis by LML, and XMS represents a fall, along the long axis, between a point of each short side of the mask surface on the long axis and a point of the each short side which is apart from the long axis by LMS.
According to another aspect of the invention, there is provided a color cathode ray tube comprising: a vacuum envelope including a substantially rectangular panel having a substantially flat outer surface, an inner surface provided with a phosphor screen, and a long axis and a short axis perpendicular to each other and also to a tube axis; a shadow mask arranged in the vacuum envelope and opposed to the phosphor screen, the shadow mask including a mask main body that has a substantially rectangular mask surface and a skirt portion extending along a periphery of the mask surface, and a substantially rectangular mask frame attached to the skirt section of the mask main body, the mask surface including an effective portion opposed to the phosphor screen and provided with a plurality of electron beam passage apertures; and an electron gun provided in the vacuum envelope for emitting electron beams onto the phosphor screen through the shadow mask.
The inner surface of the panel has an effective section with a curvature, the inner surface of the panel being formed to satisfy at least one of the following relationships:
ZPH/LPHxe2x89xa60.050, 
and
ZPV/LPVxe2x89xa60.050 
where LPH represents a distance from a center of the effective section to a long axis end of the effective section, LPV represents a distance from the center of the effective section to a short axis end of the effective section, ZPH represents a fall of the effective section at the long axis end along the tube axis with respect to a level of the center of the effective section, and ZPV presents a fall of the effective section at the short axis end along the tube axis with respect to the level of the center of the effective section.
The mask frame has a pair of long side walls situated symmetrical with respect to the long axis, and a pair of short side walls situated symmetrical with respect to the short axis, at least one of each long side wall and each short side wall having a convex curved shape such that a central portion thereof projects outwardly, and satisfying at least corresponding one of the following relationships:
YFL/LFLxe2x89xa60.015, 
and
XFS/LFSxe2x89xa60.015 
where LFL represents a distance from the short axis of the effective section of the mask surface to each corner of the effective section, LFS represents a distance from the long axis of the effective section of the mask surface to each corner of the effective section, YFL represents a fall, along the short axis, between a point of each long side wall of the mask frame on the short axis and a point of the each long side wall which is apart from the short axis by LFL, and XFS represents a fall, along the long axis, between a point of each short side wall of the mask frame on the long axis and a point of the each short side wall which is apart from the long axis by LFS.
Preferably, the panel has a transmittance of 40 to 60% at the center of the effective section, and is formed to satisfy Td/Tc less than 2.5 where Tc represents a thickness of the center of the effective section, and Td represents a thickness of the panel at an effective length end of the phosphor screen.
Even if, in the color cathode ray tube constructed as above, the curvature of the outer surface of the effective section of the panel is reduced to make the outer surface almost flat, thereby reducing the curvature of the effective surface of the mask main body, the deformation of the mask main body due to an impact or vibration applied thereto during its manufacture or transport, and resonance between a sound emitted from a speaker and the mask main body when it is installed in a television set, are minimized, and the degradation of color purity due to miss landing of electron beams is reduced, thereby realizing a high display visibility.